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The functional separation of the compression cycle from the combustion cycle provides a CAES plant with many advantages compared to simple cycle (SC) and combined cycle (CC) natural gas power plants. These features translate into significant benefits for wholesale electricity traders, buyers and sellers of full requirements power, and electric utilities.

High Thermal Efficiency
The high thermal efficiency in the production mode makes CAES one of the most competitive producers of electricity.

Typical heat rates:

Click on the charts to view the larger versions.

Click to expandHigher Ramp Rates
A CAES plant is able to ramp up 2 to 3 times faster than other gas-fired plants because it is not restrained by compression requirements. The following chart illustrates the ramp rate advantage enjoyed by CAES over simple cycle (SC) and combined cycle (CC) based on 300 MW plants.

 

Click to expandStable Heat Rate at Low Capacity
CAES maintains its heat rate at low capacity factors better than simple or combined cycle - an important advantage in providing ancillary services. In order to provide most ancillary services, generators must be operated below 100% output (increasing their variable costs) to maintain responsive capacity. CAES plants experience only minimal heat rate degradation when operating as low as 50% of their generating capacity. As the neighboring chart depicts, simple and combined cycle plants suffer significant deterioration of their heat rates when operating below 80% of their generating capacity.

Click to expandHigh Output in High Ambient Temperatures
Another CAES performance advantage is its ability to maintain output during high ambient temperature conditions. Since a given volume of hot air has a lower mass than the same volume of cold air, SC and CC turbines can experience significant reductions in mass flow and output when ambient temperatures rise above 90 °F.

The air flowing into the CAES combustion turbine is at a constant temperature and pressure. Because there is no reduction in mass flow, a CAES plant produces as much power when it is 100 °F outside as when it is 40 °F. When temperatures spike and electricity is most valuable, a CAES plant can maintain its output and maximize revenue.

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